1. Field of the Invention
The present invention relates to a guide mechanism for a cylinder apparatus, for movably retaining and guiding a displacement member of the cylinder apparatus with respect to a main cylinder body.
2. Description of the Related Art
A cylinder apparatus such as a rodless cylinder has been used as a means for transporting a workpiece. Such a rodless cylinder includes a piston, which is displaceable within a main cylinder body, and a piston yoke connected to the piston, which is exposed to the outside through a slit formed on an upper surface of the main cylinder body. A slider is installed on the piston yoke. The slider is displaced in the axial direction of the main cylinder body by displacement of the piston, in order to transport the workpiece.
However, generally in the case of the rodless cylinder described above, a gap that results from dimensional dispersion of respective members may appear between the main cylinder body and the slider in some situations, wherein the gap is caused by dimensional dispersion of respective members including, for example, the slider, the piston, and the main cylinder body, when they are assembled. In such a situation, it is feared that looseness or backlash may arise when the slider is displaced along the main cylinder body.
A cylinder apparatus is known, which is provided with a guide mechanism capable of avoiding the aforementioned backlash generated in the slider. As shown in FIG. 11, the cylinder apparatus includes a piston yoke 3, which is connected to a piston and which is inserted into a cylinder tube 2. An upper surface 2a of the cylinder tube 2 is inclined so that its height is gradually lowered from a substantially central portion of the cylinder tube 2 in the widthwise direction, with a slit 4 intervening therebetween.
A first sliding member 7, which is displaceable in the widthwise direction of the cylinder apparatus 1 by means of a screw 6a that is threaded with a slider 5, is provided between the upper surface 2a of the cylinder tube 2 and a lower surface 5a of the slider 5. On the other hand, a second sliding member 8 is also provided between a lower side portion of the cylinder tube 2 and the slider 5, in the same manner as described above.
The first and second sliding members 7, 8, which are provided between the upper surface 2a of the cylinder tube 2 and the lower surface 5a of the slider 5, function as bearings when the slider 5 is displaced in the axial direction. The first and second sliding members 7, 8 are displaced by pressing them in the widthwise direction of the cylinder apparatus 1 through threaded rotation of the screws 6a, 6b. The first and second sliding members 7, 8 abut against the upper surface 2a of the cylinder tube 2 and the lower surface 5a of the slider 5, so as to press them at predetermined pressures. Accordingly, the gap therebetween may be eliminated by adjusting the spacing distance between the cylinder tube 2 and the slider 5, in order to avoid backlash of the slider 5 with respect to the cylinder tube 2 (see, for example, Japanese Laid-Open Patent Publication No. 2002-349509).
The guide mechanism of the cylinder apparatus 1 disclosed in Japanese Laid-Open Patent Publication No. 2002-349509 is constructed such that pressing forces, which are exerted by the first and second sliding members 7, 8 on the cylinder tube 2 and the slider 5, are handled by adjusting the amount of rotation (for example, tightening torque) of the screws 6a, 6b, which thereby act to displace the first and second sliding members 7, 8 in the widthwise direction. However, it is assumed that the displacement amount of each of the first and second sliding members 7, 8, i.e., the pressing force exerted on the cylinder tube 2 and the slider 5, may suddenly change when the screws 6a, 6b is rotated.
Therefore, when each of the first and second sliding members 7, 8, which function as bearings, is pressed by a predetermined pressing force against the cylinder tube 2 and the slider 5, only a narrow adjustment range for providing a desired pressing force is possible, and reproducibility of results cannot be easily obtained. Further, a worker having skilled techniques is required to perform the adjustment operation.
The dimensional dispersion of the respective members such as the cylinder tube 2, the slider 5, the piston, and the piston yoke 3 differ depending on the actual cylinder apparatus 1 in some cases. In such a situation, it is necessary that the adjustment operation be performed for adjusting the gap for each respective cylinder apparatus 1, after the assembling operation of the cylinder apparatus 1 has been completed. It is necessary that the adjustment operation be performed by an operator by rotating the screws 6a, 6b while observing the state of the gap that occurs in the cylinder apparatus 1. Therefore, the adjustment operation, which must be performed for each respective cylinder apparatus 1, is complicated. Thus, production efficiency of the cylinder apparatus 1 cannot be measurably improved.
When the cylinder apparatus 1 is used for long periods of time, the first and second sliding members 7, 8 provided for the slider 5 may become worn or abraded due to continuous contact with the cylinder tube 2, resulting in a change in the relative positional relationship between the slider 5 and the cylinder tube 2, in spite of attempts to adjust and fix the positional relationship by the first and second sliding members 7, 8. As a result, a gap appears again between the slider 5 and the cylinder tube 2 causing backlash as described above. Thus, it is necessary for the adjustment operation to be performed repeatedly.